1. Field of the Invention
The present invention relates to a panoramic viewing system and a method thereof, especially to a panoramic viewing system and a method thereof in which a panoramic reflection mirror is adopted to work with an image sensor or a projection device for allowing the sensed image or the projected image to be provided with a better resolution and brightness.
2. Description of Related Art
In the fields of photographing, image capturing and projecting, a specification of FOV (field of view) is provided, wherein the FOV is divided into horizontal FOV, a.k.a. HFOV, and vertical FOV, a.k.a. VFOV. The HFOV for a panoramic viewing system is 360 degree and the angle of the VFOV is not specified.
In the technical aspect for panoramic viewing, the light source projected on the sensitive material, CMOS image sensor or charge-coupled device (CCD) through a curved surface of a reflection mirror may be overlapped and the energy may not be evenly distributed on each array capacitor (or photodiode), so the capacitor (or the photodiode) may receive the photo energy with different intensity, or the projection density is not even and the photo energy could not be evenly distributed on the photodiode of each CMOS image sensor or charge-coupled device, thereby causing the image to be blur. The reason for the CMOS sensor or the charge-coupled device receiving the uneven density of signal charge is that curvature radius of the curved surface may cause the uneven density of the signal charge converted from the photo signal projected on the photodiode after the incident light is inputted to the CMOS image sensor or the charge-coupled device, the larger curvature radius of the curved surface would have a higher density projected to the photodiode of the CMOS sensor or the charge-coupled device, and the smaller curvature radius of the curved surface would have a lower density projected to the CMOS sensor or the charge-coupled device.
Take the U.S. Pat. No. 5,990,934 for example, which disclosed a method and a system for panoramic viewing, in which a pyramid shaped element is adopted and four cameras (or image sensors) are required. Thus, the production cost is relatively higher. And one other disadvantage thereof is that: the image closer to the central point of the reflection mirror of the pyramid shaped element has a lower resolution. The method and system disclosed in the technical report provided by Vishvjit S. Nalwa at 1996 (i.e. U.S. Pat. No. 5,539,483) is the same as the U.S. Pat. No. 5,990,934. The U.S. Pat. No. 5,793,527 discloses a high resolution viewing system in which four lenses and four cameras are adopted, for that reason the images obtained by the pyramid reflection mirror with lower resolution are enabled to be combined for forming a panoramic image with a higher resolution.
The report provided by S. K. Nayar at 1997 discloses another method of panoramic viewing, in which a reflection mirror having a parabolic-like curved surface is adopted (the curve formula can be found in the report), and only one camera (or image sensor) is adopted. The report improves a disadvantage of the U.S. Pat. No. 5,990,934 adopting too many cameras. However, the report has two disadvantages: first, the resolution of the image closer to the central point of curved surface of the reflection mirror is less even and lower, and the brightness is relatively darker; second, the panoramic image is formed in a circular area, so four corners of the image sensor are idled. At present, most of the products available in the market are manufactured by the method mentioned above.
The Taiwan Patent NO. I268102 discloses an image process unit, which is applicable in an image sensor, the image process unit includes a plurality of photodiodes arranged in the image sensor, the photodiodes are respectively formed with different photo sensing areas according to the arranged locations, wherein the photo sensing areas of the photodiodes are gradually enlarged from the central to the outer side, accordingly the low sensitivity due to the overly-large incident angle can be compensated and the quality of image capturing can be increased. However, the technical characteristic of said patent is just opposite to the requirement of panoramic viewing.
The U.S. Pat. No. 5,539,483 discloses a panoramic projection apparatus adopting a pyramid reflection mirror and four projection devices, the operational theory is the same as the U.S. Pat. No. 5,990,934, the difference between the two is that the light source is reversely operated for forming a projection system. It is because of the same operational theory and the same technical characteristic, four projection devices are required; therefore, the production cost is relatively higher. One disadvantage thereof is that: the image which is closer to the central point of the pyramid reflection mirror and projected to a screen would have a lower resolution.
In the aspect of image processing, the CMOS image sensor or the charge-coupled device utilizes the pixel elements composed by the array photodiodes for capturing image, the sensitivity of each pixel element refers as the intensity of the photo signal projected to the photodiode being converted into the signal charge. If the sensitivity of the photodiode for light is lowered, the density of the received signal charge would become lower, and the reality and the saturation of imaging capturing would be directly affected. In addition, because the array charge storage unit of the charge-coupled device or the CMOS image sensor would cause the density of the signal charge stored in different charge storing unit to be varied; thus, a part of the captured image may be blur.
Moreover, the reason for the CMOS sensor or the charge-coupled device receiving the uneven density of signal charge is that curvature radius of the curved surface may cause the uneven density of the signal charge converted from the photo signal projected on the photodiode after the incident light is inputted to the CMOS image sensor or the charge-coupled device, the larger curvature radius of the curved surface would have a higher density projected to the CMOS sensor or the charge-coupled device, and the smaller curvature radius of the curved surface would have a lower density projected to the CMOS sensor or the charge-coupled device. The attenuation effect would directly affect the image developing quality and cause the problem of relatively brighter in the center and relatively darker at the edge. With the light compensating technology, the photo signal at the edge can be enhanced through being focused by a software or microlens, or the effective area of favorable photo sensing area can be calculated with respect to the size of the image, however the effect is still very limited.
In view of the disadvantages existed in the conventional panoramic viewing system, the present invention provides a panoramic viewing system and a method thereof for improving the above-mentioned disadvantages.